The present invention relates to an exposure apparatus, exposure method, method of controlling substrate stage and method of controlling mask stage, and in particular to such apparatus and methods taking into consideration various temperature-related environmental factors of an exposure apparatus, such as the temperature changes with time which may occur in the exposure apparatus and the temperature gradients prevailing in the exposure apparatus.
Over the years, it has been continuously desired to achieve higher and higher complexity in semiconductor devices, which in turn has required higher accuracy in positioning of a photosensitized substrate and a mask in exposure apparatuses. One of the important factors affecting the accuracy in positioning of a mask and a photosensitized substrate is the ambient air temperature, which is one of the environmental factors affecting an exposure apparatus. Specifically, in an exposure apparatus including some kind of optical position measurement devices such as interferometers, instability in an ambient air temperature in the exposure apparatus may produce non-negligible air fluctuations in the optical paths of the interferometers and/or cause uneven heat expansions of various components in the apparatus such as a stage for carrying a mask and a stage for carrying a photosensitized substrate. For this reason, it has become common to house the entire exposure apparatus in a constant temperature chamber. In such a constant temperature chamber, one or more stream of temperature-controlled air is introduced therein so as to flow around the exposure apparatus, so that the apparatus may be kept at substantially a constant temperature. This may suppress undesirable temperature changes to a certain extent, which temperature changes may occur during exposure operations performed by the exposure apparatus.
However, this technique is insufficient for improving accuracy in positioning of a mask and a photo-sensitive substrate such as meets today""s requirements.
By way of example, consider an exposure apparatus of the step-and-repeat type, in which a pattern formed on a mask is transferred onto a photosensitive substrate through a step-and-repeat exposure sequence. The exposure apparatus comprises a movable substrate stage for carrying a substrate, and the substrate stage is caused to wait at a predefined position, such as the loading position for loading on/off the substrate, for a time interval during which no exposure process is performed. Also, in an exposure apparatus of the type in which a photosensitized substrate and a mask are moved in synchronism by means of a substrate stage and a mask stage, the mask stage carrying the mask is generally caused to wait at a predefined position for a time interval during which no exposure process is performed.
In either case, the exposure apparatus produces more heat (per unit of time) during an exposure process than in a waiting interval prior to the commencement of the exposure process, so that the temperatures at regions near and around the exposure apparatus may not be stable until a substantial length of time, such as some tens of minutes to several hours, has elapsed from the commencement of the exposure process. As a result, the temperatures of some components of the exposure apparatus will often change with time during an exposure process, which leads to a substantial deviation in the measurements obtained from the position measurement systems used, between those obtained just after and those obtained several hours after the commencement of the exposure process. Apparently, such deviation will cause a deterioration in accuracy in the alignment established for an exposure operation, which may result in an exposure failure.
Further, the temperature distribution within the exposure apparatus is not uniform, especially around the substrate stage and/or the mask stage, because the exposure apparatus has several heat sources which produce temperature gradients. In addition, any changes in position of the substrate stage or the mask stage may vary the courses of the air streams flowing within the exposure apparatus, which may in turn lead to variations in temperature gradients within the exposure apparatus. Therefore, if the waiting positions for the substrate stage and the mask stage are defined without taking into consideration the temperature-related environmental factors within the exposure apparatus, the stability of an exposure process has to have certain limitations imposed thereon, such as possible occurrence of significant errors in the alignment accuracy due to temperature gradients.
In view of the foregoing, it is an object of the present invention to provide an exposure apparatus which is capable of suppressing any inconveniences which could be otherwise imposed by the temperature changes with time around the exposure apparatus.
It is another object of the present invention to provide an exposure method, in which the temperature at a region near at least one of a mask having a pattern formed thereon and a photosensitized substrate onto which the pattern of the mask is to be transferred by exposure is so adjusted that any inconvenience is avoided, which could be otherwise occur due to temperature changes with time around the exposure apparatus.
It is a further object of the present invention to provide a method of controlling a substrate stage in an exposure apparatus, in which the substrate stage is caused to wait at a position in the exposure apparatus at which stability against heat is obtained, so that the temperature gradients in the exposure apparatus and the effects of any changes in these temperature gradients may be minimized.
It is a yet further object of the present invention to provide a method of controlling a mask stage in an exposure apparatus, in which the mask stage is caused to wait at a position in the exposure apparatus at which stability against heat is obtained, so that the temperature gradients in the exposure apparatus and the effects of any changes in these temperature gradients may be minimized.
It is a still further object of the present invention to provide an exposure apparatus including a control system for a substrate stage, in which the substrate stage is caused to wait at a position in the exposure apparatus at which stability against heat is obtained, so that the temperature gradients in the exposure apparatus and the effects of any changes in these temperature gradients may be minimized.
It is a still further object of the present invention to provide an exposure apparatus including a control system for a mask stage, in which the mask stage is caused to wait at a position in the exposure apparatus at which stability against heat is obtained, so that the temperature gradients in the exposure apparatus and the effects of any changes in these temperature gradients may be minimized.
According to an embodiment of the present invention, there is provided an exposure apparatus for transferring a pattern formed on a mask onto a photosensitized substrate by exposure, comprising: a temperature measurement device for measuring temperature at a region near at least one of the mask and the photosensitized substrate; and a temperature adjustment device for comparing measurement data from the temperature measurement device with a preset desired value so as to adjust, prior to an exposure process, temperature at the region near at least one of the mask and the photosensitized substrate to an equilibrium temperature which would be established during an exposure process.
In the embodiment of the present invention described above, the exposure apparatus may further comprise a decision making device for determining, based on measurement results from the temperature measurement device and the equilibrium temperature, whether an exposure process is to be performed or not. In the case where the mask and the photosensitized substrate is held on respective stages each capable of two-dimensional movement, temperature adjustment may be achieved by moving at least one of the stages. Also, the exposure apparatus may comprise a heat supply device disposed near the mask for supplying a predetermined amount of heat based on the transmittance of the mask with respect to an exposure light beam passing through the mask. Further, in the case where the exposure apparatus comprises a first position measurement device for measuring a position of the mask and a second position measurement device for measuring a position of the photosensitized substrate, the temperature measurement device may preferably comprise a first temperature sensing device disposed near the first position measurement device and a second temperature sensing device disposed near the second position measurement device.
With the embodiment of the present invention, an exposure process may be commenced after the temperature at a region near the mask and/or the temperature at a region near the photosensitized substrate has reached an equilibrium temperature which would be established during an exposure process, so that successful exposure operations may be ensured.
In the case where the temperature adjustment is achieved by moving the stage carrying the mask and/or the stage carrying the photosensitized substrate, not only the mask and the photosensitized substrate but also the surrounding components are placed under conditions which are very close to those experienced in an actual exposure process as early as in the preliminary step before the commencement of the following exposure process. In the case where a heat supply device is disposed near the mask for supplying a predetermined amount of heat based on the transmittance of the mask with respect to an exposure light beam passing through the mask, the temperature adjustment at a region near the mask may be quickly achieved. More-over, by using the temperature measurement device to measure the temperature at a region near the first position measurement device for measuring a position of the mask as well as to measure the temperature at a region near the second position measurement device for measuring a position of the photosensitized substrate, and by adjusting the temperatures at these regions, any variations in the references for alignment of the mask and the photosensitized substrate may be suppressed, which variations could be otherwise caused by the temperature changes with time which may occur during an exposure process. This results in a significant improvement in accuracy in alignment of the mask and the photosensitized substrate.
According to an embodiment of the present invention, there is provided a method of transferring a pattern formed on a mask onto a photosensitized substrate by exposure, the method comprising the step of: adjusting, prior to an exposure process, a temperature at a region near at least one of the mask and the photosensitized substrate to an equilibrium temperature which would be established during an exposure process. The temperature adjustment may be achieved by performing a mimic exposure process, or alternatively, by supplying a stream of gas to a region near at least one of the mask and the photo-sensitized substrate, the gas having a temperature which achieves the equilibrium temperature which would be established during an exposure process.
With the embodiment of the present invention described above, the temperature at a region near the mask and/or the temperature at a region near the photosensitized substrate is/are adjusted, prior to an exposure process, to the equilibrium temperature which would be established during an exposure process, so that the temperatures of the components around the mask and/or the photosensitized substrate scarcely change even after a long-time exposure process is continued. Thus, no error is introduced in the mask and/or the photosensitized substrate or in the precision components disposed around them by the temperature changes with time which could otherwise occur.
In the case where the temperature adjustment is achieved by performing a mimic exposure process, not only the mask and the photosensitized substrate but also the surrounding components are placed under the conditions which are very close to those experienced in an actual exposure process as early as in the preliminary step before the commencement of the following exposure process. Further, in the case where a stream of temperature-controlled gas is supplied to a region near the mask and/or the photosensitized substrate, the adjustment of the temperature of the mask and/or the photosensitized substrate may be quickly achieved.
According to an embodiment of the present invention, there is provided a method of controlling a substrate stage in an exposure apparatus, the substrate stage being capable of holding thereon and moving therewith a substrate onto which a given pattern is to be transferred by exposure, the method comprising the step of: causing the substrate stage to wait, for a waiting interval during which no control sequence for exposure of the substrate on the substrate stage is performed, at a position in the exposure apparatus at which stability against heat is obtained. The position in the exposure apparatus at which stability against heat is obtained may be determined as a temporal average of the positions of the substrate stage over a time interval during which the control sequence for exposure of the substrate on the substrate stage is performed.
Such a method may comprise the steps of: determining, based on temperatures measured by each temperature sensors, average temperatures at a plurality of regions on the substrate stage over a time interval during which a control sequence for exposure of the substrate on the substrate stage is performed; determining average temperature positions which are such positions of the substrate stage that correspond to respective average temperatures of the temperature sensors; determining an average position of the average temperature positions; and causing the substrate stage to wait at the average position. Alternatively, such a method may comprise causing the substrate stage to sequentially circulate among the average temperature positions, which are such positions of the substrate stage that correspond to respective average temperatures of the temperature sensors, so as to place the substrate stage in a wait state. The present invention further provides a method of controlling a mask stage in an exposure apparatus, in which the waiting position for the mask stage is determined in the same manner.
According to an embodiment of the present invention, there is provided an exposure apparatus including a control system for a substrate stage capable of holding thereon and moving therewith a substrate onto which a given pattern is to be transferred by exposure, wherein the control system comprising: a plurality of temperature sensors, disposed at a plurality of regions on the substrate stage, for sensing ambient air temperatures in a time interval during which a control sequence for exposure of the substrate on the substrate stage is performed; an arithmetic operation device for determining an average temperature of the temperatures measured by each of the temperature sensors, determining average temperature positions which are such positions of the substrate stage that correspond to respective average temperatures of the temperature sensors, and determining an average position of the average temperature positions; and a drive device for causing the substrate stage to wait at the average position.
With the embodiments, the substrate stage is caused to wait at a position in the exposure apparatus at which stability against heat is obtained, so that any effects of the temperature gradients in the exposure apparatus on the next exposure process may be substantially eliminated. More specifically, the substrate is caused either to wait at a position which corresponds to a temporal average of the positions of the substrate stage over a time interval during which a control sequence for exposure of a substrate on the substrate stage is performed or to sequentially circulate among the average temperature positions, so that the substrate stage may be placed under the same temperature conditions as experienced during an actual exposure process, even in a waiting interval during which no exposure process is performed.
According to an embodiment of the present invention, there is provided an exposure method in which, during a predetermined period of time during which exposure control operations are suspended, at least one of the substrate stage and the mask stage is moved so as to trace its movement in an actual operation in which exposure control operations are conducted. In the above-mentioned exposure method of the present invention, it is preferred to perform irradiation of exposure light during the predetermined period of time during which exposure control operations are suspended, in the same manner as in the actual operation.
An exposure apparatus according to an embodiment of the present invention, used in the above-mentioned method comprises:
an illumination device which irradiates a mask with exposure light;
a movable mask stage adapted to hold the mask thereon;
a movable substrate stage adapted to holding a photosensitive substrate thereon;
a mask stage-moving device which moves the mask stage;
a substrate stage-moving device which moves the substrate stage; and
a controller which controls at least one of the substrate stage-moving device and the mask stage-moving device during a predetermined period of time during which exposure control operations are suspended, to thereby move at least one of the substrate stage and the mask stage in a manner such that movement of the at least one of the substrate stage and the mask stage in an actual operation in which exposure control operations are conducted is traced. In the exposure apparatus of the present invention, it is preferred that the controller controls the illumination device so as to perform irradiation of the exposure light in the same manner as in the actual operation. It is more preferred that the exposure apparatus further comprise a temperature sensor which measures a temperature of at least one site on the substrate stage and the amount of the exposure light irradiated by the illumination device be controlled by the controller, based on a measurement value of temperature of the temperature sensor.
In the embodiment of the present invention arranged as mentioned above, when the substrate stage or the mask stage is moved during a predetermined period of time during which exposure control operations are suspended (hereinafter, frequently referred to simply as xe2x80x9cstandby periodxe2x80x9d), in a manner such that movement of the substrate stage or the mask stage in an actual operation in which exposure control operations are conducted (hereinafter, frequently referred to simply as xe2x80x9cactual operationxe2x80x9d) is traced, temperature conditions in an area including the substrate stage and the mask stage during the standby period become very close to those in the actual operation, due to temperature gradient changes which are caused by the movement of the substrate stage or the mask stage. Further, in the present invention, when irradiation of exposure light is performed during the standby period in the same manner as in the actual operation, the temperature conditions during the standby period become substantially the same as those in the actual operation, because not only temperature gradient changes due to movement of the substrate stage or the mask stage, but also temperature changes due to absorption of energy of exposure light occur.
According to an embodiment of the present invention, there is provided an exposure apparatus for transferring a pattern formed on a mask to a photosensitive substrate, comprising:
an illumination device which irradiates the mask with exposure light;
a movable mask stage adapted to hold the mask thereon;
a movable substrate stage adapted to hold the photosensitive substrate thereon;
a mask stage-moving device which moves the mask stage;
a substrate stage-moving device which moves the substrate stage; and
a controller which controls at least one of the substrate stage-moving device and the mask stage-moving device during a predetermined period of time during which exposure control operations are suspended, to thereby move at least one of the substrate stage and the mask stage in a manner such that movement of the at least one of the substrate stage and the mask stage in an actual operation in which exposure control operations are conducted is traced.
According to an embodiment of the present invention, there is also provided a method for determining a standby position of at least one of a substrate stage and a mask stage in an exposure apparatus provided in a chamber, comprising the steps of:
measuring an internal temperature of the chamber; and
determining a thermally stable standby position of the at least one of the substrate stage and the mask stage, based on a measurement value of temperature obtained in the measuring step.
According to an embodiment of the present invention, there is also provided a method for determining a standby position of a wafer stage in an exposure apparatus, comprising the steps of:
determining a plurality of positions at which the wafer stage is held when exposure control operations with respect to the wafer stage are conducted;
determining the time during which the wafer stage is held at each of the plurality of positions;
determining an average position of the plurality of positions relative to the time; and
determining the average position as the standby position.
According to an embodiment of the present invention, there is also provided a method for determining a standby position of a reticle stage in an exposure apparatus, comprising the steps of:
determining a plurality of positions at which the reticle stage is held when exposure control operations with respect to the reticle stage are conducted;
determining the time during which the reticle stage is held at each of the plurality of positions;
determining an average position of the plurality of positions relative to the time; and
determining the average position as the standby position.
According to an embodiment of the present invention, there is also provided a method for controlling an exposure apparatus, the exposure apparatus having a wafer stage for performing exposure of a plurality of wafers,
the plurality of wafers being adapted to be successively provided on the wafer stage and irradiated with exposure light,
comprising the steps of:
determining a first time point at which exposure of one of the plurality of wafers is completed;
determining a second time point at which the one wafer after exposure is replaced by another wafer;
determining an average position of a plurality of positions of the wafer stage when exposure control operations with respect to the wafer stage are conducted,
the determination of the average position being made, relative to the time during which the wafer stage is held at each of the plurality of positions; and
holding the wafer stage at the average position during the period of time between the first time point and the second time point.
According to an embodiment of the present invention, there is also provided a method for controlling an exposure apparatus, the exposure apparatus having a wafer stage and a reticle stage for performing exposure of a plurality of wafers,
the plurality of wafers being adapted to be successively provided on the wafer stage and irradiated with exposure light,
comprising the steps of:
determining a first time point at which exposure of one of the plurality of wafers is completed;
determining a second time point at which the one wafer after exposure is replaced by another wafer;
determining an average position of a plurality of positions at which the reticle stage is held when exposure control operations with respect to the reticle stage are conducted,
the determination of the average position being made, relative to the time during which the reticle stage is held at each of the plurality of positions; and
holding the reticle stage at the average position during the period of time between the first time point and the second time point.
According to an embodiment of the present invention, there is also provided a standby position-determining device for determining a standby position of a wafer stage in an temperature sensors;
a calculating part which calculates an average temperature value of each of the plurality of temperature sensors, based on the information on the measurement values of temperatures stored in the memory; and
a controller which drives the wafer stage-moving device to thereby move the wafer stage and determines average-temperature positions of the wafer stage at each of which the measurement value of temperature of the temperature sensor becomes the average temperature value of the temperature sensor, with respect to each of the plurality of temperature sensors,
wherein the calculating part determines an average position of the average-temperature positions of the wafer stage, and the controller determines the average position as a standby position of the wafer stage and moves the wafer stage to the average position when exposure control operations are suspended.
According to an embodiment of the present invention, there is also provided an exposure apparatus for transferring a pattern formed on a reticle to a wafer, comprising:
a movable reticle stage for holding the reticle thereon;
a reticle stage-moving device which moves the reticle stage;
a plurality of temperature sensors provided on the reticle stage to perform measurements of temperatures when exposure apparatus, comprising:
a temperature sensor provided on the wafer stage; and
a calculating part which determines a thermally stable standby position of the wafer stage, based on a measurement value of temperature of the temperature sensor.
According to an embodiment of the present invention, there is also provided a standby position-determining device for determining a standby position of a reticle stage in an exposure apparatus, comprising:
a temperature sensor provided on the reticle stage; and
a calculating part which determines a thermally stable standby position of the reticle stage, based on a measurement value of temperature of the temperature sensor.
According to an embodiment of the present invention, there is also provided an exposure apparatus for transferring a pattern formed on a reticle to a wafer, comprising:
a movable wafer stage adapted to hold the wafer thereon;
a wafer stage-moving device which moves the wafer stage;
a plurality of temperature sensors provided on the wafer stage to perform measurements of temperatures when the wafer stage is moved in an actual operation in which exposure control operations are conducted;
a memory which stores therein information on measurement values of temperatures of the plurality of the reticle stage is moved in an actual operation in which exposure control operations are conducted;
a memory which stores therein information on measurement values of temperatures of the plurality of temperature sensors;
a calculating part which calculates an average temperature value of each of the plurality of temperature sensors, based on the information on the measurement values of temperatures stored in the memory; and
a controller which drives the reticle stage-moving device to thereby move the reticle stage and determines average-temperature positions of the reticle stage at each of which the measurement value of temperature of the temperature sensor becomes the average temperature value of the temperature sensor, with respect to each of the plurality of temperature sensors,
wherein the calculating part determines an average position of the average-temperature positions of the reticle stage, and the controller determines the average position as a standby position of the reticle stage and moves the reticle stage to the average position when exposure control operations are suspended.
According to an embodiment of the present invention, there is also provided an exposure apparatus for transferring a pattern formed on a reticle to a wafer, comprising:
a movable wafer stage adapted to hold the wafer thereon;
a wafer stage-moving device which moves the wafer stage;
a plurality of temperature sensors provided on the wafer stage to perform measurements of temperatures when the wafer stageiis moved in an actual operation in which exposure control operations are conducted;
a memory which stores therein information on measurement values of temperatures of the plurality of temperature sensors;
a calculating part which calculates an average temperature value of each of the plurality of temperature sensors, based on the information on the measurement values of temperatures stored in the memory; and
a controller connected to the wafer stage-moving device to move the wafer stage in a predetermined order between average-temperature positions of the wafer stage during a period of time during which exposure control operations are suspended,
the average-temperature positions of the wafer stage being the positions at each of which the measurement value of temperature of the temperature sensor becomes the average temperature value of the temperature sensor, with respect to each of the plurality of temperature sensors.
According to an embodiment of the present invention, there is further provided an exposure apparatus for transferring a pattern formed on a reticle to a wafer, comprising:
a movable reticle stage adapted to hold the reticle thereon;
a reticle stage-moving device which moves the reticle stage;
a plurality of temperature sensors provided on the reticle stage to perform measurements of temperatures when the reticle stage is moved in an actual operation in which exposure control operations are conducted;
a memory which stores therein information on measurement values of temperatures of the plurality of temperature sensors;
a calculating part which calculates an average temperature value of each of the plurality of temperature sensors, based on the information on the measurement values of temperatures stored in the memory; and
a controller connected to the reticle stage-moving device to move the reticle stage in a predetermined order between average-temperature positions of the reticle stage during a period of time during which exposure control operations are suspended,
the average-temperature positions of the reticle stage being the positions at each of which the measurement value of temperature of the temperature sensor becomes an average temperature value of the temperature sensor, with respect to each of the plurality of temperature sensors.
The embodiment of the present invention arranged as mentioned above is advantageous in that temperature gradient changes in the exposure apparatus are minimized, so that an operation of exposure can be stably conducted.